Recently, disk recording and reproducing devices have been used for various applications, for example, DVD, MD, CD, CD-ROM, etc., and devices having a high density, small size, high performance, high quality, and high added value have been demanded. In particular, in the magneto-optical disk recording and reproducing device using a magneto-optical media capable of recording, the demands of devices for data and devices for image-recording tend to greatly increase. Consequently devices having a small size, thin shape, high performance and high recording density have been increasingly demanded.
Hitherto, a great deal of investigations concerning the techniques of an optical head and magnetic head for a magneto-optical disk has been reported.
Hereinafter, a conventional magneto-optical head and magnetic head for magneto-optical disk will be described with reference to the drawings.
FIG. 8 is a schematic view showing a light path of a conventional magneto-optical disk recording and reproducing device.
As shown in FIG. 8, the light beam irradiated from a semiconductor laser 1 is converted into a parallel light beam by a collimator lens 2 and is separated into a plurality of different parallel light fluxes by a diffraction grating 3. A plurality of different parallel light fluxes pass through a beam splitter 4a of a composite element 4 and are converged on an information recording medium 6 having a magneto-optical effect as a main beam. The main beam has a diameter of about 1 .mu.m by means of an object lens 5 incorporated in an object lens holder 33 (see FIG. 10). At the same time, a preceding beam and a following beam as sub-beams are produced at constant intervals in front of and behind the main beam on the same track as that of the main beam by so-called three-beam method.
Moreover, a parallel light flux reflected from the beam splitter 4a of the composite element 4 is incident on a light receiving element 7 for monitoring, and thereby the driving current of the semiconductor laser 1 is controlled.
The light beam reflected from the information recording medium 6 travels in the opposite direction, is reflected from and splitted by the beam splitter 4a of the composite element 4 and then is incident on a polarization separating element 4b of the composite element 4. The semiconductor laser 1 is provided in such a way that the polarization direction of the laser beam is parallel with respect to the paper. The polarization direction of the incident light beam is rotated by 45.degree., and then the incident light beam is separated into three different fluxes having two polarization components crossing at right angles by the polarization separating element 4b, and then reflected from a mirror 4c of the composite element 4.
The reflected light beam that passes through the composite element 4 is incident on a cylindrical-shaped convex lens 8 to form a convergent light beam. Then, the convergent light beam is incident on a concave cylindrical lens 9. Herein, the concave cylindrical lens 9 is provided in such a way that the lens effect is exhibited in the direction of approximately 45.degree. with respect to the image of the recording track of the information recording medium 6 that is present in the direction of W1 in a plane being parallel to the paper.
The light beam that passes through the concave cylindrical lens 9 generates astigmatism, which is an error signal detected by a focus error signal detecting means. The light beam being incident on a plane that does not have the lens effect of the concave cylindrical lens 9 passes through an optical path shown by solid lines and is converged in a focal point 12. On the other hand, the light beam being incident on a plane that has the lens effect of the concave cylindrical lens 9 passes through an optical path shown by broken lines and is converged in a focal point 13.
A multi-divided photo-detector 10 is located in such a way that its light receiving face is approximately midway between the focal point 12 and the focal point 13.
The magnetic head is located above the information recording medium 6. The electric current is applied to the coil 26 from the current applying means 29, and thereby the magnetic field is generated.
FIG. 9 is a schematic view showing a multi-divided photo-detector and a signal detecting circuit.
As shown in FIG. 9, the multi-divided photo-detector 10 comprises a quadrant region 19 of receiving light beam, a region 20 of receiving preceding beam, a region 21 of receiving following beam, and regions 22a and 22b of receiving information signals. These light receiving regions are connected to a subtractor 23 and an adder 24. Herein, the quadrant region 19 of receiving light beam receives a light spot 16 of the main beam (P+S polarization), the region 22a of receiving information signals receives a light spot 15 of the main beam (S polarization), the region 22b of receiving information signals receives a light spot 14 of the main beam (P polarization), the region 20 of receiving preceding beam receives a light spot 17 of the preceding beam of the sub-beams, and the region 21 of receiving following beam receives a light spot 18 of the following beam of the sub-beams, respectively.
The focus error signal is detected by so-called astigmatism method. In the astigmatism method, the sums of electric signals generated at two diagonals of the quadrant region 19 of receiving light beam of the central part are calculated, and then the difference thereof is calculated. The tracking error detection signal is detected by so-called three-beam method. In the three-beam method, the difference between the light spot 17 of the preceding beam and the light spot 18 of the following beam is calculated. Furthermore, the magneto-optical disk information signal can be detected by the differential detection method. In the differential detection method, the difference between the main beam 14 comprising P polarization and the main beam 15 comprising S polarization is calculated. Furthermore, by calculating the sums thereof, a prepit signal also can be detected.
FIG. 10 is a schematic view showing a configuration of a conventional disk recording and reproducing device.
As shown in FIG. 10, the object lens 5 located below the information recording medium 6 is held by the object lens holder 33. The object lens holder 33 is fixed to an optical housing 11 using an object lens driving device 32. On the other hand, a coil 26, a yoke 27 and a slider 30 that are located above the information recording medium 6 are precisely fixed to the optical housing 11 using a suspension 28 and a suspension holder 31. The optical housing 11 can be moved in the radial direction of the information recording medium 6 by means of a carrying means 34 such as a ball screw. Moreover, the information recording medium 6 can be rotated by a spindle motor 25.
When signals are recorded on the information recording medium 6, the coil 26 and yoke 27 are held at a predetermined distance from the surface of the information recording medium 6 by the spring pressure of the suspension 28. Subsequently, in a state where the temperature on the information recording medium 6 is increased by light spot, electric current is applied to the coil 26 by a current applying means 29 (see FIG. 8). Thus, the vertical magnetic field is generated in accordance with the direction of the applied current and the vertical magnetic field is provided to the information recording medium 6 by the magnetic circuit comprising the yoke 27. Thus, the signals are recorded on the information recording medium 6.
However, in the above-mentioned conventional structure, in a case where the object lens 5 is displaced in the radial direction of the information recording medium 6 due to the decentering of the information recording medium 6 or a tracking follow-up servo by only the object lens driving device 32, or in a case where the object lens 5 is displaced due to the self-weight displacement of the object lens driving device 32, etc., the position of the coil 26 and the yoke 27 is displaced relative to the position of the object lens 5. As a result, the magnetic field strength is lowered and the recording performance is greatly deteriorated. Moreover, because the entire magnetic head is located opposite to the object lens 5 and the information recording medium 6 is sandwiched between the magnetic head and the object lens 5, as the radius of the information recording medium 6 is increased, the size of the suspension 28 is increased. As a result, it is difficult to realize devices having a small size and thin shape.